pH dependence of the photoluminescence of Eu³⁺-Intercalated layered titanium oxide

We investigated the pH dependence of Eu³⁺ emissions from Eu ³⁺-intercalated layered titanium oxide (Eu/TiO) and evaluated the local structure of the intercalated Eu³⁺ at varying pH values using lifetime measurements and EXAFS. A red Eu³⁺ emission was observed under radiation by Uv light with a higher energy than the band gap of the host TiO_x layer. The emission is based on energy transfer from the host TiO_x layer to Eu³⁺. The emission intensity of Eu/TiO in 0.01 M NaOH aqueous solution was stronger than that in 0.01 M HCl aqueous solution, and the emission response of the Eu/TiO film was relatively stable to pH cycling. Two phenomena may provide a mechanism for the change in emission from Eu/TiO. One is a change in the efficiency of energy transfer from the TiO_x nanosheet to Eu³⁺, and the other is a fine hydration state change of Eu³⁺ without a change in the total water amount.